I want to make some Suggestions.
About things you should be able to do inside the U-boats.

Eat-sleep-repeat
You crew member should be able to eat food.

but more fun is that you can try and get some sleep , wake a other resting character, that can man your station.
in game a character could be getting sleepy and gets slightly blurry vision if you don't let him rest.
when it's *red alert the main characters wake up and man their stations!(off course )

Sickness, cuts and bruises
it is very common inside a submarine to bumb your head or scratch your skin.
getting injured during battle
So playing a the boat doctor can be funny as well
doing task as healing characters, or making sure a sick crew member gets well soon. so that he can help the torpedo loading crew again.
can be a fun thing to do when you are waiting for some action.

Things break
Stuff breaks from time to time!
Repairing stuff can be challenging and fun to do.
after battle damage you should be able to repair your stuff

Be a officer!
maybe you should be able to discipline your non player-crew members!

Maybe down the track there could be an addon that gives you the ability for 1 player to command one of the destroyers against 4 sub crew . How fun would it be to pop the periscope up and see subsim player name on the destroyer .

1- It could be REALLY nice to include a .pdf manual with some basics phraseology so we can talk in proper manner when issuing an order or acknowledge one... (SHIII & SHV give us some tips about it but there's always room to improve I think).

2- May be a leaderboard that show who's the Captain with more sinked tonnage?

3- Some kind of awards/medals when you reach specific milestones in the sim?

4- Some kind of penalitation when you don't follow the Captain orders that's also linked with your profile, so you know what kind of "sailor" is joining the party.